When a physician is assessing a patient who may be experiencing acute myocardial infarction or ischemia, the physician needs accurate data quickly to properly diagnose the patient, and most importantly, to provide the appropriate treatment.
The current "state of the art" methods for detecting or confirming acute myocardial infarction or ischemia involve the considering of a combination of factors. This diagnosing can include analyzing cardiac enzymes such as creatinine phosphokinase (CPK), analyzing the patient's electrocardiogram (ECG), in addition to analyzing patient signs and symptoms.
Unfortunately, these methods have an inherent time delay to acquire the data, thus delaying any treatment decision which relies on the data. For example, sequential enzyme assays and ECGs both consume precious time. As will be discussed in more detail below, the delay of even a few minutes can greatly decrease the effectiveness and benefits associated with therapies such as thrombolytic drugs.
Furthermore, extensive training and experience is required to accurately interpret ECGs. Even with such extensive training and experience, ECG findings can be nonspecific.
Although cardiac catheterization is accurate and reliable, in most cases it is not available in a timely fashion in that it requires both proper medical facilities and a cardiologist and is thus typically impractical.
Studies have shown that both the short term benefit and the long term benefit achieved by thrombolytic therapy are closely related to the therapy's early initiation. However, although thrombolytic therapy has a relatively large benefit-to-risk ratio, its associated risks of hemorrhage, especially intracerebral hemorrhage, mandates that a high probability exists for acute myocardial ischemia or infarction to be present before thrombolytic therapy is used.
Currently, the average time between a patient's arrival in an emergency room and the initiation of thrombolytic therapy is slightly greater than one hour. The necessary acquisition or interpretation of multiple laboratory tests by a physician after the patient arrives in the emergency department accounts for the greatest percentage of this time. Reducing the time to initiate thrombolytic therapy will require diagnostic testing which is rapid, relatively sensitive and specific for acute myocardial infarction and ischemia. Such testing will require a minimum of patient cooperation and will yield results which require a limited amount of skill and experience.
What is needed, then, is a practical, accurate, quick and relatively inexpensive method of diagnosing acute myocardial infarction and ischemia, which can reduce the time between the initial contact with a patient and the time the patient receives appropriate therapy.
The prior art listed on the appended list of prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant's acknowledged duty to disclose relevant prior art. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
Yelderman, U.S. Pat. No. 5,095,913 is directed to a capnograph for measuring the absolute concentrations of constituents in a patient's respiratory air stream.
Walls et al., U.S. Pat. No. 4,169,465 is directed to a method and apparatus for obtaining cardio-pulmonary measurements using a rebreathing technique. A patient breathes a gas containing selected trace gases in a closed system. The concentrations of these trace gases is detected and recorded over time.
Neither Yelderman nor Walls et al. discloses that cardiovascular distress produces a telltale substance which may be detected in a patient's expired air stream. Furthermore, neither reference discloses apparatus for detecting such a substance.